Back-fire trap for rectifiers or converters



May 17, 1932. w BOHRAU? 1,858,616

BACK FIRE TRAP FOR RECTIFIERS' OR CONVERTERS Filed May 50, 1930 [Wt enter (#120202 46M flttormy.

Patented May 17, 1932 UNITED STATES BACK-FIRE TRAP FOR REGTIFIER$ 01R CONVERTERS Application filed May 30, 1930. Serial n. 457,560.

In such electrical converters as the mercury vapor are, where a characteristic unilateral conductivity of a space current is utilized to rectify alternating currents, it frequently happens in practice that such conditions arise as cause a loss of the unilateral conductivity characteristic. The tube impedance falls with the result that the current rises. The apparatus is consequently endangered and the service interrupted unless some protective device is in the circuit.

Commonly such protective devices function as chokes which by virtue of their reactance retard the building up of unduly large currents and their proper operation is dependent upon the time-constant of the circuit being adapted to prevent the occurrence of persisting back-fire arcs within the tube under varying conditions of impressed voltage wave form and load impedance. It may so happen that under particular conditions of load and impressed voltage a given prior art device functions properly but such devices frequently fail due to the fact that the ratio of apparent resistance to reactance is incorrect.

The object of my invention is to lessen the number of failures due to the above mentioned cause. It is a well known fact that as the load on a reactor is varied the ratio of reactance to resistance may change due to changes in the permeability of the core and other such like phenomena. The essence of my invention lies in the control of this characteristic of converter back-fire traps such as shown in the drawing herewith for the purpose of determining the proper ratio of resistance to reactance so that back-fire arcs shall be suppressed.

In this drawing, 1 is a full-wave rectifier of the mercury vaportypeconnected as shown to the source of single phase alternating current 2. 8 is the load to carry pulsating unidirectional current. 4: and 5 are conventional reactances to maintain the arc in continuous operation. a, a and b, b are pairs of anodes connected as shown. 0 is the cathode of the rectifier.

The anodes a and a are identical in shape and so located within the tube that normally the space current path a 0 has the same electrical dimensions as has a 0. In the same manner the path I; 0 is similar to Z2 0.

' The choking reactanc'es are shown as 6, 7, 8 and 9, 10, 11. To the end that the ratio of resistance to reactance in such a circuit may have a proper value I introduce the unique supplementary windings l2 and 13 across whose terminals the non-inductive resistances 1 and 15 are connected as shown.

While the tube is functioning properly, current in the portion of the circuit 0 a 6 7 sets up flux in the reactor 6 8 which is exactly neutralized by flux due to current in the portion of the circuit'c a" 8 7 Similarly, under the same conditions of normal operation, the resulting flux linking the reactor 9, 11 is also zerov andthe system may be considered as having two simplerectifiers a b c and a Z) 0 in parallel, each with the same load as the other andoperating in an entirely identical manner. 7

Under normal working conditions the resultant magnetic flux linking either winding 12 or winding 13 is Zero. There is no current flowing-through either of the resistors 14: or

15 so that the efiiciency of the system is not lowered by the use of my invention under normal operating conditions. When, however,

a back-fire occurs the resultant flux in the reactors is not zero. Current flows through the resistively loaded windings 12 and 13. Losses are introduced whose magnitude may be controlled to some extent by the values assigned to the resistors 14 and 15. Thus by the use of the invention controlis gained of the losses in the trap reactors and it is pos- 'sible to fix upon a proper value of these losses so that the ratio of resistance to reactance in theback-fire chokes is such as to insure the proper functioning of those protecreactance in converter back-fire traps come within the scope of my invention. Hence I being centre tapped to the circuit and connected to the anodes by separate leads.

Signed at Montreal, Province of Quebec, Canada, the 19th day of May, 1930.

, WERNER BOHRAUS.

of anodes connected to a common circuit, re-

actances interposed in the portion of the circuit leading to said anodes, said reactances I being connected in parallel from said circuit to the anodes so as to compose separate circuits for the latter, each reactance including an auxiliary winding inductively coupled to the primary reactance, and non-inductive resistance coupled to said primary reactance.

2. The combination with a rectifier or converter, of a back-fire trap consisting of a pair of anodes connected to a common circuit, choking reactances interposed in the portion of the circuit leading to said anodes, said reactances being connected in parallel from said circuit to the anodes so as to compose separate circuits for the latter, supplement ary windings constituting a part of said reactances, and non-inductive resistance connected to the terminals of said windings.

3. The combination with a rectifier or converted provided with anodes arranged in pairs, each pair being connected to a common circuit, of center-tapped reactances connected to the circuit of each pair of anodes, supplementary windings constituting a part of said reactances, and non-inductive resistance connected to the terminals of said Windings.

4:. The combination in a rectifying system in which a pair of anodes are connected to a common circuit, of a reactor in the circuit in which the ratio of apparent resistance to reactance is controlled by an auxiliary Windbeing centre tapped to the circuit and con-- nected to the anodes by separate leads.

6. The combination in a rectifying system in which a pair of anodes are connected to a common circuit, of a reactor in the circuit in which the ratio of apparent resistance to reactance is controlled by mechanically varying the magnetic circuit to alter the saturation and permeability of the core and thus the time-constant of the reactor, said reactor 

